Fourteen-year-old Fia originates from Datania. She flees Datania alongside Shu during their second escape attempt, successfully joining the Returners group. Though shy and discreet, Fia possesses considerable willpower. Her time with the Returners hides a secret: she acts as a spy for Nines. Betrayed by Nines, she remains with Shu and the Returners. However, Fia lacks DT, a special substance essential within humans, preventing her from continuing the journey. She stays under the care of nomads residing in a large mobile land craft. Following the cataclysmic tidal wave that floods the world, Fia is identified as the group's only confirmed survivor.